Recently, in the field of a magnetic disc drives, it is required to further improve a recording density of the magnetic disc. In the conventional in-plane magnetic recording system, magnetization is recorded onto a recording surface of the magnetic disc in a parallel direction. On this account, if a recording interval narrows, a thermal fluctuation effect of recording magnetization cannot be ignored. Accordingly, a perpendicular magnetic recording system has been suggested as a method for enabling a higher recording density. Since the magnetization is recorded onto the recording surface of the magnetic disc in a perpendicular direction according to the perpendicular magnetic recording system, the recording magnetization is rarely affected by the thermal fluctuation effect. Therefore, the recording interval of the magnetization can be narrowed.
A magnetic head adopting the perpendicular magnetic recording system is called a single pole head. In such a single pole head, the magnetization is recorded onto the recording surface of the magnetic disc in a perpendicular direction by using a main pole having a magnetic pole surface which is opposed to the recording surface of the magnetic disc so as to emit a record magnetic field onto the recording surface.
Since the magnetic head rotates over the recording surface of the magnetic disc substantially along the radius direction of the magnetic disc in the state where the magnetic head is held by a distal end of a head assembly, the direction of the magnetic head is often inclined with respect to the direction of a track (hereinafter, the angle of such an inclination is simply referred as a skew angle). Here, the direction of the magnetic head refers to the rotational radius direction of rotation movement.
FIG. 15 is an explanatory diagram illustrating a state of the magnetic pole surface disposed on a track formed on the recording surface (the conventional example). As shown in the drawing, among tracks formed on the recording surface, in a track 102A where the skew angle becomes zero, a magnetic pole surface 101 is included in the width of the track 102A. On the other hand, in a track 102B where the skew angle increases, a magnetic pole surface 101 is not included in the width of a track 102B. In this way, when the recoding is performed in the state where the magnetic pole surface 101 is not included in the width of the track 102B, boundary portions between adjacent tracks are magnetized to cause noise at the time of a reproducing process, or the adjacent tracks themselves are magnetized to cause a data erase (hereinafter, such a phenomenon is referred to as a side erase).
In Japanese Patent Publication No. 2004-94997 (“Patent Document 1”), there is disclosed a technology in which the side erase is prevented by modifying the shape of the magnetic pole surface of the main pole. However, according to the technology, in order to prevent the side erase in the entire tracks included in the recording surface, the profile of the magnetic pole surface is excessively decreased. As a result, it is impossible to secure the amount of a record magnetic field generated by the magnetic pole surface to a sufficient level, thereby deteriorating recording characteristics.